1. Field of the Invention
The present invention relates to a disc player adapted to selectively read first and second layers formed in a disc, the first layer having recorded therein multi-bit digital signal obtained by sampling with a sampling signal Fs while the second layer has recorded therein one-bit digital signal obtained by sampling with a sampling signal nxc3x97Fs (n is an integer larger than 2).
The present invention relates also to a disc player adapted to selectively read first and second types of discs, the first type of disc having recorded therein multi-bit digital signal obtained by sampling with a sampling signal Fs while the second type of disc has recorded therein one-bit digital signal obtained by sampling with a sampling signal nxc3x97Fs (n is an integer larger than 2).
2. Description of Related Art
Generally, a disc player for playback of optical discs, typically, compact discs (CD; will be referred to as xe2x80x9cCD discxe2x80x9d hereinafter for the convenience of illustration and explanation), comprises an optical pickup to read information recorded with pits in the disc, RF amplifier to amplify RF signal, servo control circuit, mechanical drive circuit, digital signal processing circuit, DA converter, analog audio circuit, etc.
For playback of an optical disc, a laser light is first generated at the optical pickup, it is irradiated onto the disc, and the RF amplifier produces various servo signals based on a reflected light from the disc surface. The servo control signals include a focus servo signal according to which the laser is focused onto a pit on the disc, a tracking servo signal to allow the laser spot focused on the disc surface to track a succession of pits, a spindle servo signal which is a clock component extracted from a signal produced by binary-coding of an RF signal and according to which the disc rotation or spinning is controlled, and a sled servo signal to allow the optical pickup to move radially of the disc.
After the servo control circuit and mechanical drive circuit operate correctly, a signal read from the disc is subjected to EFM demodulation (eight-fourteen demodulation) in the digital signal processing circuit, has an error corrected, and then it is subject to digital/analog conversion in the DA converter to provide an analog audio signal.
Recently, however, a standard for high-density recording optical discs as new audio optical discs has been proposed which are different from that for the conventional CD discs.
The high-density recording optical discs (will be referred to as xe2x80x9cHD discxe2x80x9d hereinafter) prescribed in the standard is adapted to record one-bit audio signal produced by a delta-sigma (xcex94xcexa3) modulation of analog audio signal.
In the delta-sigma modulation, a signal is converted using an extremely high sampling frequency, for example, a frequency 64 times higher than the sampling frequency of 44.1 kHz for the conventional CD discs.
The one-bit signal will be referred to as xe2x80x9chigh speed one-bit audio signalxe2x80x9d hereinafter.
In the delta sigma modulation, a very high frequency is used to sample a signal and a quantization bit is represented by one bit having a very short data length, so that the transmission frequency bandwidth for the delta sigma modulation is wide.
Also in the delta sigma modulation, a high dynamic range can be assured in an audio bandwidth lower than the oversampling frequency 64 times higher than the sampling frequency for the conventional CD discs.
Audio signals conforming to the above standard will be referred to as xe2x80x9cHD signalxe2x80x9d hereinafter. The specifications of a conventional CD disc and HD disc will be described with reference to Table 1 below.
As seen from Table 1, the HD disc has the same diameter and thickness of 12 cm and 1.2 mm, respectively, as the conventional CD.
In the optical recording/reproduction system for the CD signal, the read wavelength is 780 nm, standard scanning speed (relative linear velocity) is 1.25 m/s, shortest pit length is 0.87 xcexcm and track pitch is 1.6 xcexcm.
On the other hand, in the optical recording/reproduction system for the HD signal, the read wavelength is 650 nm, standard scanning speed (relative linear velocity) is 3.94 m/s, shortest pit length is 0.4 xcexcm and track pitch is 0.74 xcexcm.
For signal processing, the PCM (pulse code modulation) method is used for the CD signal while the DSD (direct stream digital) method is used for the HD disc. The standard sampling frequency for the CD signal is 44.1 kHz, and that for the HD signal is 2.8224 MHz for multiple quantization bits. The number of quantization bits is 16 for the CD signal but 1 for the HD signal.
Further, the modulation method adopted for the CD signal is EFM while that for the HD signal is EFM+1. Also, the ECC (error correction coding) method for the CD signal recording disc is CIRC (cross interleave Reed-Solomon coding), and that for the HD disc is PC (product code)-RS (Reed-Solomon).
Therefore, a disc player compatible with both CD and HD discs (will be referred to as xe2x80x9cCD/HD playerxe2x80x9d hereinafter) will be considered below. Since both the HD disc and CD disc have the same shape, a disc rotation driving mechanism can be used in common to drive them. Therefore, the spindle/sled servo control system is compatible with both the HD disc and CD disc.
However, since the optical recording/reproduction and signal processing methods for the HD disc are different from those for the CD disc, an optical pickup, RF amplifier, and signal processing circuits for modulation, DA conversion, etc. for the HD disc should be uniquely designed for each of the HD and CD discs. An analog audio circuit can be used for both the HD and CD discs if the disc player has a single output terminal.
Thus, such CD/HD players have been proposed each of which has common circuits for both the discs and dedicated circuits for the respective discs.
However, only a single disc can be set and played in the CD/HD player at a time. When a CD disc, for example, is played in the CD/HD player, the dedicated circuits for the other type of disc, namely, an HD disc, are also always energized and in active status unless any countermeasures are taken. The disc player as a whole will consume a larger amount of power, and the active status of the dedicated circuits for the other type of disc will cause the disc player to malfunction and cause a noise to adversely affect the circuits in operation for the disc being played in the disc player.
Especially in a CD/HD player designed for a high-fidelity audio playback, clock oscillation at the dedicated circuits for the type of disc other than currently played in the player will have an adverse affect on the reproduced sound quality.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing a disc player compatible with more than one type of audio optical disc having signals recorded thereon based on the different optical recording methods, respectively, and which can be driven by the same driving mechanism, the disc player being adapted to control, during playback of a selected one of the different types of discs, the signal processing system for the other type of disc not currently being played to stand in a power saving mode in order to minimize the power consumption of the disc player as a whole, and prevent malfunction of the circuitry being energized but not in use for the disc currently being played and a noise from coming into the circuitry used for the disc currently being played.
The above object can be attained by providing a disc player to selectively read a first digital signal of m quantization bits (m is an integer larger than or equal to 2) sampled with a sampling frequency Fs (Hz) and a second digital signal of one quantization bit sampled with a sampling frequency nxc3x97Fs (Hz) (n times of the sampling frequency Fs (Hz); n is an integer larger than or equal to 2), the disc player comprising according to the present invention:
a first means for processing the first digital signal;
a second means for processing the second digital signal; and
means for providing, during reading either of the first and second digital signals, a control to minimize the power consumption of the signal processing means for the other digital signal.
Also the above object can be attained by providing a player for a disc-like recording medium having a first layer having recorded thereon a first digital signal of m quantization bits (m is an integer larger than or equal to 2) sampled with a sampling frequency Fs (Hz) and a second layer having recorded thereon a second digital signal of one quantization bit sampled with a sampling frequency nxc3x97Fs (Hz) (n times of the sampling frequency Fs (Hz); n is an integer larger than or equal to 2), the player comprising according to the present invention:
means for selecting either of the first and second layers for signal read therefrom;
a first means for processing the first digital signal recorded on the first layer;
a second means for processing the second digital signal recorded on the second layer; and
means for providing, during reading the digital signal recorded on one of the first and second layers selected by the selecting means, a control to minimize the power consumption of the signal processing means for the digital signal recorded on the other layer.
Also the above object can be attained by providing a disc playback method of selectively reading a first type of disc having recorded thereon a first digital signal of m quantization bits (m is an integer larger than or equal to 2) sampled with a sampling frequency Fs (Hz) and a second type of disc having recorded thereon a second digital signal of one quantization bit sampled with a sampling frequency nxc3x97Fs (Hz) (n times of the sampling frequency Fs (Hz); n is an integer larger than or equal to 2), the method comprising, according to the present invention, the steps of:
discriminating a disc going to be read between the first and second types;
controlling, when the disc is judged to be the first type one, a signal processing system for the second digital signal to stand in a power saving mode; and
controlling, when the disc is judged to be the second type one, a signal processing system for the first digital signal to stand in a power saving mode.
In the above disc player and method, since either of the digital audio signals or either of the discs cannot be read at a time, the signal processing system for the other digital audio signal or disc has not to be in the active status. Therefore, according to the present invention, the signal processing system for the disc or audio signal not currently being read is controlled to stand in the power saving mode.
These objects and other objects, features and advantages of the present intention will become more apparent from the following detailed description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings.